This invention relates in general to compression techniques and, more particularly, to techniques for efficiently compressing image information on a real-time basis.
A substantial amount of information is required to digitally define a single two-dimensional image, such as a photograph or a video image. Such an image is typically represented in the form of an array of several thousand pixels, each of which requires a certain amount of associated information to set forth a gray scale or color value for that pixel. In a video context, where there is a sequence of successive images, the amount of information required to represent the entire sequence can be enormous.
A first issue relates to situations where video information is to be stored. The amount of storage space needed corresponds directly to the amount of information which must be stored and, as mentioned above, the amount of information can be enormous. A second issue relates to situations where video information must be transmitted to a remote location. Each type of communication link, such as a telephone line or a radio channel, has limits on the amount of information that can be transmitted therethrough within a specified interval of time. In a real-time application, the amount of video information may exceed these limits. It is therefore desirable to compress video information, both to reduce the amount of storage space that would be needed to save the video information, and also to reduce the amount of information that would have to be transmitted through a communication link during a given interval of time.
Various techniques for video compression have already been developed. For example, one known technique is time lapse recording, which involves temporal sampling. In particular, selected images are saved, and other images are discarded. For example, every tenth image may be saved, and other images discarded. A different known approach involves spatial sampling, where each image is subsampled in order to reduce the number of pixels, and thus reduce the amount of overall information. In many applications, only a portion of an image is of primary interest, and other portions are of secondary interest. However, these known techniques of temporal and/or spatial sampling involve a uniform loss of resolution in time or space throughout the image information.
Other techniques have been developed to try to effect compression in a non-uniform manner within a given image, in particular by saving more information as to portions of the image which are of interest, and less information as to portions of the image which are of less interest. However, in order to determine which portion of an image is of greatest interest, these techniques typically use automated analysis of the image itself, and this approach sometimes is gives priority to a portion of the image which is not of primary interest.
Thus various techniques of video compression have already been developed, and have been generally adequate for their intended purposes. However, they have not been satisfactory in all respects.
From the foregoing, it may be appreciated that a need has arisen for a method and apparatus for effecting compression of image information in an efficient manner on a real-time basis, with the capability to reliably identify portions of an image which are of primary interest and which can be given priority for purposes of compression. According to the present invention, a method and apparatus are provided to address this need, and involve generating image information regarding a selected scene using an image detector, generating supplemental information regarding the selected scene using a supplemental detector, and generating compressed information by processing the image information as a function of the supplemental information, the supplemental information being different from the image information.